With an increase in capacity of information processing in recent years, various information recording technologies have been developed. In particular, the surface recording density of an HDD using magnetic recording technology is continuously increasing at an annual rate of approximately 100%. In recent years, an information recording capacity exceeding 320 gigabytes/platter with a 2.5-inch diameter of a perpendicular magnetic recording medium for use in an HDD or the like has been desired. To fulfill such demands, an information recording density exceeding 500 gigabits/inch square is desired to be achieved.
To attain a high recording density in a magnetic recording medium for use in an HDD or the like, a perpendicular magnetic recording type has been suggested in recent years. In a perpendicular magnetic recording medium for use in the perpendicular magnetic recording type, the axis of easy magnetization of a recording layer is adjusted so as to be oriented in a direction perpendicular to the base surface. In the perpendicular magnetic recording type, compared with a conventional in-plane recording type, it is possible to more suppress a so-called thermal fluctuation phenomenon, in which thermal stability of a recording signal is impaired because of a superparamagnetic phenomenon to cause the recording signal to be lost, and therefore the perpendicular magnetic recording type is suitable for increasing the recording density.
Various important factors for increasing recording density of the perpendicular magnetic recording medium include an improvement in magnetostatic characteristic, such as a coercive force Hc and a reversed magnetic domain nucleation magnetic field Hc; an improvement in electromagnetic conversion characteristic, such as an overwrite characteristic (OW characteristic) and an SNR (Signal to Noise Ratio); and narrowing of a track width. Among all, an improvement in coercive force Hc and an improvement in SNR are important for reading and writing accurately at high speed even at a recording bit of a small area.
An improvement in SNR is achieved mainly by reducing noise in a magnetization transition region of the magnetic recording layer. Effective factors for reducing noise include an improvement in crystal orientation of the magnetic recording layer, making a finer particle diameter of each magnetic particle, and isolation of the magnetic particles. Among all, making a finer particle diameter is effective at reducing noise in the magnetization transition region of a boundary of recording bits.
Also in recent years, magnetic recording medium devices are often used not only for a conventional purpose as storage devices for personal computers but also for mobile purposes such as portable telephones and car navigation systems. With such diversification of use purposes, reliability under harsh environments and a further improvement in recording and reproducing characteristic have become problems in magnetic recording media.
To solve the problems above, for example, Patent Document 1 discloses a method of manufacturing a magnetic recording medium in which after a heating process of heating a substrate where a magnetic recording layer is formed is performed, a protective film forming process of forming a carbon protective film by plasma CVD is performed. According to the method described in Patent Document 1, a perpendicular magnetic recording medium having an excellent recording and reproducing characteristic can be obtained, and also a dense carbon protective film excellent in adhesiveness can be formed. Therefore, a magnetic recording medium having such a recording and reproducing characteristic and reliability both can be provided.